Urea concentration identification device for urea solution

ABSTRACT

A urea concentration identification device comprising a concentration identification sensor unit ( 2 ) and a support unit ( 4 ) attached at the bottom end thereof with this sensor unit and provided at the top end thereof with a mounting unit ( 4   a ) to a urea solution tank opening. The concentration identification sensor unit ( 2 ) has an indirectly-heated concentration detector and liquid temperature detector provided with metal fins ( 21   c ),( 22   c ), respectively, for heat-exchanging with urea solution. The concentration identification sensor unit ( 2 ) is provided with a cover member ( 2   d ) that forms an opposite-ends-opened urea solution induction passage so as to surround the metal fins ( 21   c ),( 22   c ), and an enclosure ( 2   e ) that forms communication holes ( 26 ),( 27 ) in the top and bottom end plate thereof ( 2   e   1 ),( 2   e   2 ). A single-pulse voltage is applied to the heating element of the indirectly-heated concentration detector to heat it, and a urea concentration is identified at an identification operation unit based on an output from a concentration detection circuit including the temperature sensing element of the indirectly-heated concentration detector and the liquid temperature detector.

This application is a 371 of PCT/JP2004/013213 filed on Sep. 10, 2004,published on Mar. 24, 2005 under publication number WO 2005/026709 A1which claims priority benefits from Japanese Patent Application Number2003-319775 filed Sep. 11, 2003.

TECHNICAL FIELD

The present invention relates to a device for identifying a ureaconcentration in urea solution which is to be sprayed to exhaustpurification catalyst so as to decompose nitrogen oxides (NOx) in asystem to purify exhaust discharged from an internal-combustion engineof an automobile, etc.

BACKGROUND ART

In an internal-combustion engine of an automobile, fossil fuel such asgasoline or gas oil is burnt. Exhaust that is generated along with thecombustion includes, together with water and carbon dioxide,environmental pollutants such as unburned carbon monoxide (CO) andcarbon hydride (HC), sulfur oxides (SOx), and nitrogen oxides (NOx).Recently, especially for environmental protection and to prevent livingenvironment from being polluted, there are suggested variouscountermeasures to purify exhaust from an automobile.

As one countermeasure, there is known the use of an exhaust purificationcatalyst device. According to this device, three way catalyst forexhaust purification is arranged on the way of an exhaust system, whereCO, HC, NOx and the like are decomposed by oxidation-reduction to berendered harmless. In order to continuously keep decomposing NOx in thecatalyst device, urea aqueous solution is sprayed to the catalyst fromthe upstream side of the catalyst device of the exhaust system. The ureaaqueous solution has to have its concentration set to be in a specificurea concentration range so as to enhance the effect of decomposing NOx,and particularly a urea concentration of 32.5% is considered to be mostdesirable.

Urea solution, which is stored in a urea solution tank carried on anautomobile, may have its concentration changed as time goes by, andfurthermore, there may be raised unevenness in concentrationdistribution locally in the tank. Urea solution, which is to be suppliedto a spray nozzle from the tank through a supply-pipe by means of apump, is generally taken out from an outlet port located near the bottomof the tank. Thus, urea solution around the area has to be of a desiredurea concentration so as to enhance the efficiency of the catalystdevice.

On the other hand, conventionally, a urea concentration in urea solutionis not directly measured. Furthermore, in an exhaust system, there isemployed a method of arranging NOx sensors at the upstream side as wellas at the downstream side of a catalyst device, and judging whether ornot decomposition of NOx is suitably carried out based on the differenceof NOx concentrations detected by these sensors. However, this method isemployed to measure the effect of actual reduction of NOx, and cannotidentify a urea concentration not only before spraying urea solution butalso from the very beginning of spraying urea solution. Moreover, NOxsensors used in this method are not sufficient in sensitivity forrealizing spraying urea solution of a desired concentration.

In Patent Document 1, there is disclosed a fluid identification methodof making a heating element generate heat by applying current thereto,heating a temperature sensing element using thus generated heat,exerting a thermal influence on heat transfer from the heating elementto the temperature sensing element by means of fluid to be identified,and determining the kind of the fluid to be identified based on anelectric output corresponding to an electric resistance of thetemperature sensing element, in which method current is applied to theheating element periodically.

However, since current is applied to the heating element periodically(with multiple pulses), this fluid identification method is required totake considerable time for identification, which makes it difficult toidentify the fluid instantly. Furthermore, under this method, even iffluid identification can be carried out using a representative value formaterials whose properties are significantly different from each othersuch as water, air, oil, it is difficult to identify a ureaconcentration correctly and promptly by applying this method to theabove-described urea concentration identification for urea solution.

Moreover, in order to improve the reliability of an exhaust purificationprocessing system, it is desired that concentration identification forurea solution be carried out frequently and appropriate processing beperformed. Accordingly, it may be necessary to carry out concentrationidentification for urea solution while an automobile is moving. Underthis condition, identification precision is generally lowered ascompared with that in the case under static condition. It is importantto suppress the lowering of precision as much as possible to make itpossible to correctly carry out concentration identification.

Patent Document 1: JP(A)-11-153561 (especially paragraphs [0042] to[0049])

DISCLOSURE OF THE INVENTION

Accordingly, the present invention has an object to overcome theabove-mentioned drawbacks by providing an identification device for ureasolution which can identify a urea concentration in urea solutioncorrectly as well as promptly.

Furthermore, the present invention has another object to provide anidentification device for urea solution which can carry outconcentration identification even under shaking condition.

According to the present invention, there is provided a ureaconcentration identification device for identifying a urea concentrationin urea solution stored in a tank, comprising a concentrationidentification sensor unit; and a support unit having one end to whichthe concentration identification sensor unit is attached and the otherend provided with a mounting unit to be attached to an opening of thetank,

wherein the concentration identification sensor unit includes anindirectly-heated concentration detector having a heating element and atemperature sensing element, and a liquid temperature detector formeasuring the temperature of urea solution; the indirectly-heatedconcentration detector has a heat transfer member for concentrationdetector for exchanging heat with the urea solution; the liquidtemperature detector has a heat transfer member for liquid temperaturedetector for exchanging heat with the urea solution; and a cover memberis attached to the concentration identification sensor unit so as tosurround the heat transfer member for concentration detector and theheat transfer member for liquid temperature detector to form a ureasolution induction passage with its both ends opened, the urea solutioninduction passage extending in the longitudinal direction of the supportunit, which is directed from one end to the other end thereof,

wherein the concentration identification sensor unit is provided with anenclosure which three-dimensionally encloses the periphery of the ureasolution induction passage without covering both the ends of the ureasolution induction passage; the enclosure is provided with a firstcommunication hole and a second communication hole formed on one endplate and the other end plate thereof separated in the longitudinaldirection, respectively; the first and second communication hole arelocated away from the extension of the urea solution induction passageso as to allow the urea solution to pass therethrough; and the secondcommunication hole is so provided as to be separated away from a linewhich passes through the first communication hole and extends in thelongitudinal direction, and

wherein a single-pulse voltage is applied to the heating element of theindirectly-heated concentration detector to make the heating elementgenerate heat, and an identification operation unit identifies the ureaconcentration based on an output of a concentration detection circuitincluding the temperature sensing element of the indirectly-heatedconcentration detector and the liquid temperature detector.

According to an aspect of the present invention, the one end plate andthe other end plate of the enclosure are separated away from both endsof the urea solution induction passage by 3 mm or more. According to anaspect of the present invention, the first communication hole and thesecond communication hole have their longer diameters set to be 10 mm orlower. According to an aspect of the present invention, the enclosure isin the form of a cylinder with the one end plate and the other end platecorrespond to both end surfaces.

According to an aspect of the present invention, the identificationoperation unit identifies the urea concentration using a concentrationcorrespondence voltage value corresponding to the difference between theinitial temperature and the peak temperature of the temperature sensingelement when the heating element generates heat. According to an aspectof the present invention, as a voltage value corresponding to theinitial temperature of the temperature sensing element, an averageinitial voltage value which is obtained by sampling the initial voltagebefore starting the application of the single-pulse voltage to theheating element by a predetermined number of times and calculating theaverage thereof is used, and as a voltage value corresponding to thepeak temperature of the temperature sensing element, an average peakvoltage value which is obtained by sampling the peak voltage beforeending the application of the single-pulse voltage to the heatingelement by a predetermined number of times and calculating the averagethereof is used, and as the concentration correspondence voltage value,the difference between the average peak voltage value and the averageinitial voltage value is used.

According to an aspect of the present invention, a liquid temperaturecorrespondence output value corresponding to the liquid temperature ofthe urea solution is input from the liquid temperature detector to theidentification operation unit, and the identification operation unitidentifies the urea concentration, using calibration curves indicativeof the relation between the liquid temperature and the concentrationcorrespondence voltage value prepared for a plurality of reference ureasolutions whose urea concentrations are different from each other andgiven in advance, based on the liquid temperature correspondence outputvalue and the concentration correspondence voltage value obtained forurea solution to be identified.

According to an aspect of the present invention, the identificationoperation unit has a microcomputer. According to an aspect of thepresent invention, a circuit board constituting the concentrationdetection circuit is arranged on the other end of the support unit, anda wire runs inside the support unit to electrically connect theconcentration identification sensor unit to the circuit board. Accordingto an aspect of the present invention, the microcomputer is arranged ona circuit board.

According to the present invention, since a urea concentration isidentified for urea solution stored in a tank, a concentrationidentification sensor unit is arranged inside the tank, and ureaconcentration identification with desirable precision can be stablyperformed without being affected by external environmental conditions.

Furthermore, according to the present invention, since a ureaconcentration is identified at an identification operation unit based onan output of a concentration detection circuit by applying asingle-pulse voltage to a heating element of an indirectly-heatedconcentration detector to make the heating element generate heat, a ureaconcentration in urea solution can be identified correctly as well aspromptly. Especially, if a urea concentration is identified using aconcentration correspondence voltage value corresponding to thedifference between the initial temperature and the peak temperature of atemperature sensing element when the heating element generates heat, andthe difference between an average peak voltage value and an averageinitial voltage value is used as the concentration correspondencevoltage value, correct as well as prompt identification can be performedstably.

Furthermore, according to the present invention, since a cover membersurrounds a heat transfer member for concentration detector and a heattransfer member for liquid temperature detector to from a urea solutioninduction passage with its both ends opened, urea-solution around theheat transfer members has difficulty in raising a forced flow based on aforeign factor, which can improve the precision of the above-describedconcentration identification.

Especially, according to the present invention, since an enclosure isarranged at a concentration identification sensor unit, and a firstcommunication hole and a second communication hole are formed atspecific positions on specific plates of the enclosure, lowering of theprecision of identification can be reduced even if the tank is undershaking condition.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an exploded perspective view of one embodiment of the ureaconcentration identification device according to the present invention;

FIG. 2 shows a sectional view of the urea concentration identificationdevice part of which is omitted;

FIG. 3 shows a view indicative of the state of mounting the ureaconcentration identification device to a tank;

FIG. 4 shows an enlarged view of an indirectly-heated concentrationdetector and a liquid temperature detector;

FIG. 5 shows a sectional view of the indirectly-heated concentrationdetector of FIG. 4;

FIG. 6 shows an exploded perspective view of a thin film chip of theindirectly-heated concentration detector;

FIG. 7 shows a block diagram of a circuit for identifying aconcentration;

FIG. 8 shows a view indicative of the relation between a single-pulsevoltage P applied to a heating element and a sensor output Q,

FIG. 9 shows an example of calibration curves;

FIG. 10 shows an example of a liquid temperature correspondence outputvalue T;

FIG. 11 shows an example of the relation between a concentrationcorrespondence voltage value V0 and an actual concentration;

FIG. 12 shows an example of the relation between a concentrationcorrespondence analog output voltage value V0′ and an actualconcentration;

FIG. 13 shows an example of the relation between a liquid temperaturecorrespondence analog output voltage value T′ and an actual temperature;

FIG. 14 shows a result of an experiment carrying out concentrationidentification;

FIG. 15 shows a result of an experiment carrying out concentrationidentification;

FIG. 16 shows a result of an experiment carrying out concentrationidentification;

FIG. 17 shows a result of an experiment carrying out concentrationidentification;

FIG. 18 shows a result of an experiment carrying out concentrationidentification;

FIG. 19 shows a result of an experiment carrying out concentrationidentification; and

FIG. 20 shows a result of an experiment carrying out concentrationidentification;

wherein reference numeral 2 denotes a concentration identificationsensor unit, 2 a basal body, 2 b,2 c O-ring, 2 d cover member, 2 eenclosure, 2 e 1 upper plate, 2 e 2 lower plate, 2 e 3 side plate, 21indirectly-heated concentration detector, 22 liquid temperaturedetector, 23 mold resin, 24 urea solution induction passage, 26,27communication hole, 21 a thin film chip, 21 b jointing material, 21 c,22c metal fin, 21 d bonding wire, 21 e, 22 e external electrode terminal,21 a 1 basal plate, 21 a 2,22 a 2 temperature sensing element, 21 a 3inter-layer insulating film, 21 a 4 heating element, 21 a 5 heatingelement electrode, 21 a 6 protective film 21 a 7 electrode pad, 4support unit, 6 circuit board, 8 cover member, 10,14 wire, 12 connector,64, 66 resistor, 68 bridge circuit, 70 differential amplifier, 71 liquidtemperature detection amplifier, 72 microcomputer, 74 switch, 76 outputbuffer circuit, 100 urea solution tank, 102 opening, 104 ureaconcentration identification device, 106 inlet pipe, 108 outlet pipe,110 urea solution supply pump, and US denotes a urea solution.

BEST MODE FOR CARRYING OUT THE INVENTION

The present invention will further be described below concerning thebest modes with reference to the accompanying drawings.

FIG. 1 shows an exploded perspective view of one embodiment of the ureaconcentration identification device according to the present invention,FIG. 2 shows a sectional view of the same, part of which is omitted, andFIG. 3 shows a view indicative of the state of mounting the same to atank.

As shown in FIG. 3, a urea solution tank 100 for decomposing NOx, whichconstitutes an exhaust purification system carried on an automobile,etc., is provided with an opening 102 on the top thereof, and a ureaconcentration identification device 104 according to the presentinvention is mounted to the opening 102. To the tank 100, an inlet pipe106 from which urea solution is let in and an outlet pipe 108 from whichurea solution is taken out are fixed. The outlet pipe 108 is coupled tothe tank 100 at a height located near the bottom thereof, and is coupledto a urea solution spray unit, not shown, through a urea solution supplypump 110. In an exhaust system, the urea solution spray unit arrangedright before an exhaust purification catalyst device sprays ureasolution to the catalyst device.

The urea concentration identification device 104 includes aconcentration identification sensor unit 2 and a support unit 4. Theconcentration identification sensor unit 2 is attached to one end(bottom portion) of the support unit 4, and the other end (top portion)of the support unit 4 is provided with a mounting unit 4 a to beattached to the opening 102 of the tank 100.

The concentration identification sensor unit 2 includes anindirectly-heated concentration detector 21 that has a heating elementand a temperature sensing element, and a liquid temperature detector 22that measures the temperature of urea solution. The indirectly heatedconcentration detector 21 and the liquid temperature detector 22 arearranged in the up and down direction with a predetermined distancesituated therebetween. FIG. 4 shows an enlarged view of theindirectly-heated concentration detector 21 and the liquid temperaturedetector 22, and FIG. 5 shows a sectional view of the same.

As shown in those figures, the indirectly-heated concentration detector21 and the liquid temperature detector 22 are united by a mold resin 23.As shown in FIG. 5, the indirectly-heated concentration detector 21includes a thin film chip 21 a having a heating element and atemperature sensing element, a metal fin 21 c working as a heat transfermember for concentration detector which is coupled to the thin film chip21 a through a jointing material 21 b, and external electrode terminals21 e which are electrically connected to an electrode of the heatingelement and an electrode of the temperature sensing element of the thinfilm chip 21 a through a bonding wire 21 d. The liquid temperaturedetector 22 has similar structure, and includes a metal fin 22 c workingas a heat transfer member for liquid temperature detector and externalelectrode terminals 22 e.

FIG. 6 shows an exploded perspective view of the thin film chip 21 a ofthe indirectly-heated concentration detector 21. For example, the thinfilm chip 21 a has a basal plate 21 a 1 made of Al₂O₃, a temperaturesensing element 21 a 2 made of Pt, an inter-layer insulating film 21 a 3made of SiO₂, a heating element 21 a 4 made of TaSiO₂ and a heatingelement electrode 21 a 5 made of Ni, a protective film 21 a 6 made ofSiO₂, and electrode pads 21 a 7 made of Ti/Au, which are layered in thisorder. The temperature sensing element 21 a 2 is formed into ameandering pattern, which is not shown. The liquid temperature detector22 has a thin film chip 22 a of similar structure, and does not make aheating element work but makes only a temperature sensing element 22 a 2work.

As shown in FIG. 1 and FIG. 2, the concentration identification sensorunit 2 has a basal body 2 a mounted to the bottom end portion of thesupport unit 4, and O-rings 2 b are used when mounting the basal body 2a. To the side of the basal body 2 a, the mold resin 23 uniting theindirectly-heated concentration detector 21 and the liquid temperaturedetector 22 is attached through an O-ring 2 c. To the basal body 2 a, acover member 2 d is so attached as to surround the fin 21 c forconcentration detector and the fin 22 c for liquid temperature detector.The cover member 2 d forms a urea solution induction passage 24 thatextends in the up and down direction, passing through the fin 21 c forconcentration detector and the fin 22 c for liquid temperature detectorsequentially, with its both upper and lower ends opened. Since the covermember 2 d is attached to the basal body 2 a, a flange portion of themold resin 23 is pressed toward the basal body 2 a, which fixes the moldresin 23 to the basal body 2 a.

On the top portion of the support unit 4, a circuit board 6 constitutinga concentration detection circuit to be described later is arranged, anda cover member 8 is so mounted as to cover the circuit board 6. As shownin FIG. 2, inside the support unit 4, a wire 10 runs to electricallyconnect the indirectly-heated concentration detector 21 and liquidtemperature detector 22 of the concentration identification sensor unit2 to the circuit board 6. The circuit board 6 has a microcomputerarranged thereon that works as an identification operation unit to bedescribed later. Through a connector 12 attached to the cover member B,a wire 14 is provided for carrying out communication between the circuitboard 6 and the outside. The identification operation unit may bearranged not on the circuit board 6 but outside the cover member 8, inwhich case the circuit board 6 and the identification operation unit areconnected through the wire 14.

As shown in FIG. 1 and FIG. 2, the concentration identification sensorunit 2 has an enclosure 2 e that three-dimensionally encloses theperiphery of the urea solution induction passage 24, desirably with apredetermined distance of 3 mm or more situated therebetween, withoutcovering both the upper and lower ends of the urea solution inductionpassage 24. The enclosure 2 e is in the form of a cylinder and has aplanar upper plate 2 e 1, a planar lower plate 2 e 2, and a cylindricalside plate 2 e 3. The center portion of the upper plate 2 e 1 is coupledto the basal body 2 a by welding, etc. The upper plate 2 e 1 is providedwith a first communication hole 26 through which urea solution can pass,while the lower plate 2 e 2 is provided with a second communication hole27 through which urea solution can pass. These communication holes 26,27 are located away from the extension of the urea solution inductionpassage 24, and the second communication hole 27 is so provided as to beseparated away from a line which passes through the first communicationhole 26 and extends in the longitudinal direction (up and downdirection) of the support unit 4. For example, the communication holes,26, 27 are circular openings whose diameters are 10 mm or lower, and incase the holes are openings other than circular openings, longerdiameters are 10 mm or lower.

For example, the enclosure 2 e has its horizontal (X direction and Ydirection) dimension (diameter) set to be 50 to 100 cm, and has its upand down dimension (height) set to be 80 to 150 cm. On the other hand,the urea solution induction passage 24 has its up and down dimension setto be 1 to 4 cm.

The enclosure 2 e prevents the inside of the urea solution inductionpassage 24 from being affected even if a flux is raised in urea solutionin the tank 100 when the tank 100 is shaken, so that precision ofconcentration identification is not significantly lowered, whichprocessing will be described later. In case the dimension of theenclosure 2 e is too large, a flux is easily raised in urea solutioninside the enclosure 2 e undesirably. On the other hand, in case longerdiameters of the communication holes 26, 27 are too large, a flux raisedin urea solution is prone to affect the inside of the urea solutioninduction passage 24. Furthermore, in case the distance between both theupper and lower-ends of the urea solution induction passage 24 and theenclosure 2 e is too short, specifically less than 3 mm, identificationprecision is prone to be lowered.

The basal body 2 a, cover member 2 d, and enclosure 2 e of theconcentration identification sensor unit 2, support unit 4, and covermember 8 are made of corrosion-proof material such as stainless steel.

FIG. 7 shows a block diagram for identifying a concentration in thepresent embodiment. The temperature sensing element 21 a 2 of theindirectly-heated concentration detector 21, the temperature sensingelement 22 a 2 of the liquid temperature detector 22, and two resistors64, 66 form a bridge circuit 68. An output of the bridge circuit 68 isinput to a differential amplifier 70, and an output of the differentialamplifier (also referred to as concentration detection circuit output orsensor output) is input to a microcomputer 72 that works as anidentification operation unit through an A/D converter, not shown. Also,the microcomputer 72 receives a liquid temperature correspondence outputvalue corresponding to the liquid temperature of urea solution from thetemperature sensing element 22 a 2 of the liquid temperature detector 22through a liquid temperature detection amplifier 71. On the other hand,the microcomputer 72 outputs a heater control signal to a switch 74located on an electric pathway to the heating element 21 a 4 of theindirectly-heated concentration detector 21 to control the opening andclosing of the switch.

Next, the performance of concentration identification in the embodimentwill be explained.

When urea solution US is stored in the tank 100, the enclosure 2 e ofthe concentration identification sensor unit 2 and the urea solutioninduction passage 24 formed by the cover member 2 d are filled with theurea solution US. When the tank 100 remains stationary, the ureasolution US not only in the urea solution induction passage 24 but alsoin the entire tank 100 substantially does not flow.

When the microcomputer 72 sends the heater control signal to the switch74 to close the switch 74 for a predetermined period of time (forexample, four seconds), a single-pulse voltage P of a predeterminedheight (for example, 10V) is applied to the heating element 21 a 4 tomake the heating element generate heat. At this time, as shown in FIG.8, an output voltage (sensor output) Q of the differential amplifier 70gradually increases when the voltage P is being applied to the heatingelement 21 a 4, and gradually decreases after the application of thevoltage P to the heating element 21 a 4 is ended.

As shown in FIG. 8, the microcomputer 72 samples the sensor output by apredetermined number of times (for example, 256 times) for apredetermined time period (for example, for one second) before startingthe application of voltage P to the heating element 21 a 4, and obtainsan average initial voltage value V1 by carrying out an operation toobtain the average value thereof. The average initial voltage value V1corresponds to the initial temperature of the temperature sensingelement 21 a 2. Furthermore, as shown in FIG. 8, the microcomputer 72samples the sensor output by a predetermined number of times (forexample, 256 times) for a predetermined time period (for example, forone second) before ending the application of voltage P to the heatingelement 21 a 4, and obtains an average peak voltage value V2 by carryingout an operation to obtain the average value thereof. The average peakvoltage value V2 corresponds to the peak temperature of the temperaturesensing element 21 a 2. Then, the difference between the average initialvoltage value V1 and the average peak voltage value V2 (=V2−V1) isobtained as a concentration correspondence voltage-value V0.

On the other hand, in the above-described method, calibration curvesindicative of the relation between the temperature and the concentrationcorrespondence voltage value V0 are obtained in advance with respect toseveral urea aqueous solutions (reference urea solutions) whose ureaconcentrations are given in advance, and thus obtained calibrationcurves are stored in a storage means of the microcomputer 72. FIG. 9shows an example of the calibration curves. In this example, calibrationcurves are prepared for reference urea solutions whose ureaconcentrations are 0%, 20%, and 40%.

As shown in FIG. 9, since the concentration correspondence voltage valueV0 depends on the temperature, when measuring a concentration of ureasolution to be measured using the calibration curves, a liquidtemperature correspondence output value T that is input from thetemperature sensing element 22 a 2 of the liquid temperature detector 22through the liquid temperature detection amplifier 71 is also used. FIG.10 shows an example of the liquid temperature correspondence outputvalue T. Such a calibration curve is also stored in the storage means ofthe microcomputer 72. Furthermore, FIG. 11 shows an example of therelation between the concentration correspondence voltage value V0 andan actual concentration obtained from urea solutions whose temperaturesand urea concentrations are different from each other.

From the liquid temperature correspondence output value T obtained forurea solution to be measured, a temperature value “t” is obtained usingthe calibration curve shown in FIG. 10. Then, concentrationcorrespondence voltage values V0 (0%; t), V0 (20%; t), and V0 (40%; t)corresponding to the temperature value “t” are obtained on therespective calibration curves shown in FIG. 9. Then, it is determinedhow much percentage of urea concentration corresponds to theconcentration correspondence voltage value V0 (X; t) obtained for ureasolution to be measured, by carrying out proportion operation using atleast two of the concentration correspondence voltage values V0 (0%; t),V0 (20%; t), and V0 (40%; t), for example, V0 (20%; t) and V0 (40%; t),on the respective calibration curves. As described above, identificationof a urea concentration can be carried out correctly as well as promptly(instantly). On the other hand, as the calibration curves shown in FIG.9, those using the liquid temperature correspondence output value Tinstead of the temperature can be employed, which can omit storing thecalibration curve shown in FIG. 10.

Then, a signal indicative of thus obtained concentration value is outputto an output buffer circuit 76 shown in FIG. 7 through a D/A converter,not shown, and is then output to a main computer (ECU), not shown, forcarrying out combustion control for an engine of an automobile as ananalog output. FIG. 12 shows an example of the relation between ananalog output voltage value V0′ corresponding to a concentration and anactual concentration. The difference with respect to temperature in thisrelation is small, which enables practical use. Furthermore, FIG. 13shows an example of the relation between an analog output voltage valueT′ corresponding to a liquid temperature and an actual temperature. Theliquid temperature correspondence analog output voltage value T′ is alsooutput to the main computer (ECU) On the other hand, signals indicativeof the concentration value and the liquid temperature value are takenout as digital outputs according to need, and are input to devices fordisplaying, alarming, and other performances.

The above-described urea concentration identification for urea solutionis based on the principle that there is a correlation between a kineticviscosity of urea solution under natural convection and a sensor output.In order to enhance the precision of concentration identification, it isdesirable that urea solution around the fin 21 c for concentrationdetector and fin 22 c for liquid temperature detector has difficulty inraising a forced flow based on a foreign factor as much as possible.From such a viewpoint, it is desirable to use the cover member 2 d,especially one having urea solution induction passage 24 extending inthe up and down direction. The cover member 2 d works also as aprotection member that prevents a foreign matter from coming intocontact therewith.

As described above, it is considered that the optimal concentration ofurea solution to be used in an exhaust purification system is 32.5%.Accordingly, setting a range between 25% to 40% as an appropriate range,an alarm may be given in case an identification result deviating fromthe appropriate range is obtained. Furthermore, in case urea in the tankis reduced and the urea solution induction passage 24 comes to beunfilled with urea solution, a concentration correspondence voltagevalue of urea solution significantly deviating from the appropriaterange is obtained in identifying a concentration, in which case arequired alarm may also be given. Similarly, in case liquid (forexample, salt solution, coolant water, etc.) whose correlation between akinetic viscosity thereof and a sensor output is different from that ofurea solution is poured into the tank by accident, a concentrationcorrespondence voltage value different from that within the appropriaterange which is obtained when using urea solution whose liquidtemperature is equal to that of thus poured liquid is obtained inidentifying a concentration, in which case a required alarm may also begiven.

Furthermore, based on the liquid temperature correspondence output valueT sent from the liquid temperature detector 22, in case it is detectedthat urea solution has its temperature reduced to a temperature aroundwhich urea solution is frozen (around −13° C.), an alarm may be given.

As in the above, the case in which the urea solution US in the tank 100is not made to forcibly flow is explained. On the other hand, in caseconcentration identification is carried out when an automobile carryingthe tank 100 is moving, there may be raised a flow in the urea solutiondue to the shaking of the tank 100. In this case, according to thedevice of the present invention, since the concentration identificationsensor unit 2 has the enclosure 2 e, even if urea solution outside theenclosure is made to flow, an influence resulting from the flow ishardly exerted on the inside of the enclosure 2 e, especially on theinside of the urea solution induction passage 24.

Concerning the shaking of the tank 100, there is shaking in the up anddown direction and shaking in the horizontal direction, and shakingwhich largely exerts an influence on the above-described concentrationidentification is shaking in the horizontal direction. This is becauseshaking in the horizontal direction largely contributes to liquid levelfluctuation and urea solution flow resulting therefrom. Theconcentration identification sensor unit 2 is arranged near the bottomof the tank, at which height the flow of urea solution has little up anddown direction components and dominating horizontal directioncomponents. Accordingly, by forming a communication hole, which is nottoo large, on each of the upper plate 2 e 1 and the lower plate 2 e 2 ofthe enclosure 2 e to enable urea solution to pass therethrough betweenthe outside of the enclosure and the inside of the enclosure, andforming no hole on the side plate 2 e 3, a flow in the horizontaldirection of liquid inside the tank and outside the enclosure isprevented from exerting an influence on the inside of the enclosure.

Furthermore, at a position where the concentration identification sensorunit 2 is arranged, there exits a flow of urea solution in the up anddown direction, which is not dominating. In this regard, by makingpositions of the communication holes 26, 27 different from each other inthe horizontal plane (in the XY plane), urea solution is prevented frompassing through the enclosure 2 e and flowing in the up and downdirection. Moreover, by making positions of the communication holes 26,27 different from that of the urea solution induction passage 24 in thehorizontal plane (in the XY plane), a flow in the up and down directionis prevented from exerting an influence on the inside of the ureasolution induction passage 24.

FIG. 14 to FIG. 20 show results of experiments carrying outconcentration identification using the concentration identificationdevice according to the present invention or a device which are used forcomparison. In these experiments, the enclosure is used or not used, andthe number and arrangement of the communication holes formed at theenclosure are different, and the others in structure of the devices aremade equal. Four liters of urea solution having urea concentration of32.5% is used. Concentration values measured under various shaking speedconditions with amplitude of 40 mm in the X direction and Y directionare shown.

In an experiment shown in FIG. 14, as the communication holes 26, 27formed at the upper plate 2 e 1 and lower plate 2 e 2, holes of 5 mm indiameter which are located at positions different from each other andalso different from that of the urea solution induction passage 24 inthe XY plane (horizontal plane) are formed, one for each platerespectively. Distances between the upper and lower end openings of theurea solution induction passage 24 and the upper and lower plates 2 e 1,2 e 2 of the enclosure are set to be 5 mm, respectively. Thisexperimental configuration is of the present invention.

In an experiment shown in FIG. 15, the enclosure is not used.

In an experiment shown in FIG. 16, as the communication holes 26, 27formed at the upper plate 2 e 1 and lower plate 2 e 2, holes of 5 mm indiameter which are located at positions equal to that of the ureasolution induction passage 24 in the XY plane (horizontal plane) areformed, one for each plate respectively. Distances between the upper andlower end openings of the urea solution induction passage 24 and theupper and lower plates 2 e 1, 2 e 2 of the enclosure are set to be 5 mm,respectively.

In an experiment shown in FIG. 17, as the communication holes 26, 27formed at the upper plate 2 e 1 and lower plate 2 e 2, holes equal tothose employed in the experiment shown in FIG. 14 are formed. On theother hand, distance between the lower end opening of the urea solutioninduction passage 24 and the lower plate 2 e 2 of the enclosure is setto be 5 nm, while distance between the upper end opening of the ureasolution induction passage 24 and the upper plate 2 e 1 of the enclosureis set to be 0 mm (that is, the upper end of the urea solution inductionpassage is covered).

In an experiment shown in FIG. 18, as the communication holes 26, 27formed at the upper plate 2 e 1 and lower plate 2 e 2, holes of 5 mm indiameter which are located at positions different from each other andalso different from that of the urea solution induction passage 24 inthe XY plane (horizontal plane) are formed, three for each platerespectively. Distances between the upper and lower end openings of theurea solution induction passage 24 and the upper and lower plates 2 e 1,2 e 2 of the enclosure are set to be 5 mm, respectively.

In an experiment shown in FIG. 19, as the communication holes 26, 27formed at the upper plate 2 e 1 and lower plate 2 e 2, holes equal tothose employed in the experiment shown in FIG. 18 are formed. On theother hand, distance between the lower end opening of the urea solutioninduction passage 24 and the lower plate 2 e 2 of the enclosure is setto be 5 mm, while distance between the upper end opening of the ureasolution induction passage 24 and the upper plate 2 e 1 of the enclosureis set to be 0 mm (that is, the upper end of the urea solution inductionpassage is covered).

In an experiment shown in FIG. 20, the experimental configuration isequal to that of the experiment shown in FIG. 19 except that there isformed no communication hole at the lower plate 2 e 2 and threecommunication holes 27′ are formed at the side plate 2 e 3.

As can be seen from the above-described results, in the experimentsshown in FIG. 15 to FIG. 20, measurement values are widely distributedas compared with those in the experiment shown in FIG. 14 (measurementvalues 25% to 40%). Thus, it can be seen that the lowering of precisioncan be lessened according to the configuration of the present invention,even if the tank is shaken.

1. A urea concentration identification device for identifying a ureaconcentration in urea solution stored in a tank, comprising: aconcentration identification sensor unit; and a support unit having oneend to which the concentration identification sensor unit is attachedand the other end provided with a mounting unit to be attached to anopening of the tank, wherein the concentration identification sensorunit includes an indirectly-heated concentration detector having aheating element and a temperature sensing element, and a liquidtemperature detector for measuring the temperature of urea solution, theindirectly-heated concentration detector has a heat transfer member forconcentration detector for exchanging heat with the urea solution, theliquid temperature detector has a heat transfer member for liquidtemperature detector for exchanging heat with the urea solution, and acover member is attached to the concentration identification sensor unitso as to surround the heat transfer member for concentration detectorand the heat transfer member for liquid temperature detector, the covermember forming a urea solution induction passage with an open upper endand an open lower end, the passage formed to allow the urea solution toflow from one of the open ends to the other of the open ends of thecover member while passing through the heat transfer member forconcentration detector and the heat transfer member for liquidtemperature detector, the urea solution induction passage extending inthe longitudinal direction of the support unit, which is directed fromone end to the other end thereof, wherein the concentrationidentification sensor unit is provided with an enclosure which threedimensionally encloses the periphery of the urea solution inductionpassage without covering both the ends of the urea solution inductionpassage, the enclosure is provided with a first communication hole and asecond communication hole formed on one end plate and the other endplate thereof separated in the longitudinal direction, respectively, thefirst and second communication hole are located away from the extensionof the urea solution induction passage so as to allow the urea solutionto pass therethrough, and the second communication hole is so providedas to be separated away from a line which passes through the firstcommunication hole and extends in the longitudinal direction, wherein asingle-pulse voltage is applied to the heating element of theindirectly-heated concentration detector to make the heating elementgenerate heat, and an identification operation unit identifies the ureaconcentration based on an output of a concentration detection circuitincluding the temperature sensing element of the indirectly-heatedconcentration detector and the liquid temperature detector, and whereinthe identification operation unit identifies the urea concentrationusing a concentration correspondence voltage value corresponding to thedifference between the initial temperature and the peak temperature ofthe temperature sensing element when the heating element generates heat.2. The urea concentration identification device for the urea solution asclaimed in claim 1, wherein the one end plate and the other end plate ofthe enclosure are separated away from both ends of the urea solutioninduction passage by 3 mm or more.
 3. The urea concentrationidentification device for the urea solution as claimed in claim 1,wherein the first communication hole and the second communication holehave their longer diameters set to be 10 mm or lower.
 4. The ureaconcentration identification device for the urea solution as claimed inclaim 1, wherein the enclosure is in the form of a cylinder with the oneend plate and the other end plate correspond to both end surfaces. 5.The urea concentration identification device for the urea solution asclaimed in claim 1, wherein as a voltage value corresponding to theinitial temperature of the temperature sensing element, an averageinitial voltage value which is obtained by sampling the initial voltagebefore starting the application of the single-pulse voltage to theheating element by a predetermined number of times and calculating theaverage thereof is used, and as a voltage value corresponding to thepeak temperature of the temperature sensing element, an average peakvoltage value which is obtained by sampling the peak voltage beforeending the application of the single-pulse voltage to the heatingelement by a predetermined number of times and calculating the averagethereof is used, and as the concentration correspondence voltage value,the difference between the average peak voltage value and the averageinitial voltage value is used.
 6. The urea concentration identificationdevice for the urea solution as claimed in claim 1, wherein a liquidtemperature correspondence output value corresponding to the liquidtemperature of the urea solution is input from the liquid temperaturedetector to the identification operation unit, and the identificationoperation unit identifies the urea concentration, using calibrationcurves indicative of the relation between the liquid temperature and theconcentration correspondence voltage value prepared for a plurality ofreference urea solutions whose urea concentrations are different fromeach other and given in advance, based on the liquid temperaturecorrespondence output value and the concentration correspondence voltagevalue obtained for urea solution to be identified.
 7. The ureaconcentration identification device for the urea solution as claimed inclaim 1, wherein the identification operation unit has a microcomputer.8. The urea concentration identification device for the urea solution asclaimed in claim 1, wherein a circuit board constituting theconcentration detection circuit is arranged on the other end of thesupport unit, and a wire runs inside the support unit to electricallyconnect the concentration identification sensor unit to the circuitboard.
 9. The urea concentration identification device for the ureasolution as claimed in claim 7, wherein the microcomputer is arranged ona circuit board.
 10. A urea concentration identification device foridentifying a urea concentration in urea solution stored in a tank,comprising: a concentration identification sensor unit including aconcentration detector having heating and temperature sensing functions,the concentration detector having a heat transfer member for exchangingheat with the urea solution; a support unit having one end to which theconcentration identification sensor unit is attached and the other endprovided with a mounting unit to be attached to an opening of the tank;and a cover member forming a urea solution induction passage extendingin the longitudinal direction of the support unit and having an openingon an upper end and an opening on a lower end, the passage formed toallow the urea solution to flow from the opening on one of the ends tothe opening on the other of the ends of the cover member while passingthrough the heat transfer member, the heat transfer member facing theurea solution induction passage, wherein the concentrationidentification sensor unit is provided with an enclosure which threedimensionally encloses the periphery of the urea solution inductionpassage without covering both the ends of the urea solution inductionpassage, wherein a single-pulse voltage is applied to the concentrationdetector to generate heat, and an identification operation unitidentifies the urea concentration based on an output of a concentrationdetection circuit including the concentration detector, and wherein theidentification operation unit identifies the urea concentration using aconcentration correspondence voltage value corresponding to thedifference between the initial temperature and the peak temperature ofthe concentration detector when the concentration detector generatesheat.
 11. The urea concentration identification device for the ureasolution as claimed in claim 10, wherein the enclosure is provided witha first communication hole and a second communication hole formed on oneend plate and the other end plate thereof separated in the longitudinaldirection of the support unit, respectively, the first and secondcommunication hole are located away from the extension of the ureasolution induction passage so as to allow the urea solution to passtherethrough, and the second communication hole is so provided as to beseparated away from a line which passes through the first communicationhole and extends in the longitudinal direction.
 12. The ureaconcentration identification device for the urea solution as claimed inclaim 10, wherein the enclosure is free of side holes through which thesensor unit is visible from outside.
 13. The urea concentrationidentification device for the urea solution as claimed in claim 10,wherein the enclosure comprises an upper end plate, a side plate and alower end plate, and the side plate has no hole.
 14. The ureaconcentration identification device for the urea solution as claimed inclaim 11, wherein the enclosure is free of side holes through which thesensor unit is visible from outside.
 15. The urea concentrationidentification device for the urea solution as claimed in claim 11,wherein the enclosure comprises an upper end plate, a side plate and alower end plate, and the side plate has no hole.